Generally, fine pattern formation is carried out by photolithography in the manufacture of a semiconductor device. A number of substrates called transfer masks (photomasks) are normally used for such fine pattern formation. The transfer mask comprises generally a transparent glass substrate having thereon a fine pattern made of a metal thin film or the like. The photolithography is used also in the manufacture of the transfer mask.
In the manufacture of a transfer mask by photolithography, use is made of a mask blank having a thin film (e.g. a light-shielding film) for forming a transfer pattern (mask pattern) on a transparent substrate such as a glass substrate. The manufacture of the transfer mask using the mask blank is carried out by a method comprising an exposure process of writing a required pattern on a resist film formed on the mask blank, a developing process of developing the resist film to form a resist pattern in accordance with the written pattern, an etching process of etching the thin film along the resist pattern, and a process of stripping and removing the remaining resist pattern. In the developing process, a developer is supplied after writing the required pattern on the resist film formed on the mask blank to dissolve a portion of the resist film soluble in the developer, thereby forming the resist pattern. In the etching process, using the resist pattern as a mask, an exposed portion of the thin film, where the resist pattern is not formed, is dissolved by dry etching or wet etching, thereby forming a required mask pattern on the transparent substrate. In this manner, the transfer mask is produced.
For miniaturization of a pattern of a semiconductor device, it is necessary to shorten the wavelength of exposure light for use in the photolithography in addition to the miniaturization of the mask pattern of the transfer mask. In recent years, the wavelength of exposure light for use in the manufacture of a semiconductor device has been shortened from KrF excimer laser light (wavelength: 248 nm) to ArF excimer laser light (wavelength: 193 nm).
As a type of transfer mask, apart from a conventional binary mask having a light-shielding film pattern made of a chromium-based material on a transparent substrate, there has recently appeared a binary mask using, as a light-shielding film, a material such as MoSiN containing a transition metal and silicon as main metal components and further containing nitrogen, as described in JP-A-2007-292824 (Patent Document 1).
In the meantime, hitherto, with respect to a transfer mask manufactured from a mask blank by forming a transfer pattern in a light-shielding film by dry etching using as a mask a resist pattern formed in a resist film by electron beam writing and development or an etching mask pattern formed in an etching mask film, a comparison is made, using a pattern inspection apparatus, between a design transfer pattern and the transfer pattern formed in the light-shielding film and a defect (so-called black defect) portion where the light-shielding film remains in excess as compared with the design transfer pattern is corrected by a physical treatment using nanomachining or focused ion beam (FIB) machining. However, there has been a problem that the correction of the black defect portion by such a physical treatment takes much time. Further, since the irradiation dose of Ga ions becomes large in the normal FIB machining, Ga stain remaining on a quartz substrate has been a problem. In view of this, there has been reported a technique of gas assist for enhancing the reactivity to suppress the Ga irradiation dose (see JP-A-2000-10260 (Patent Document 2)) or the like.
On the other hand, JP-A-2004-537758 (Patent Document 3) discloses a defect correction technique that supplies a xenon difluoride (XeF2) gas to a black defect portion of a light-shielding film and irradiates an electron beam onto the black defect portion, thereby etching the black defect portion to remove it (hereinafter, such defect correction that is carried out by irradiating charged particles such as an electron beam while supplying a fluorine-containing substance such as a xenon difluoride gas will be referred to simply as “EB defect correction”). Such EB defect correction was at first used for correction of a black defect portion in an absorber film of a reflective mask for EUV lithography, but has started to be used also for defect correction of a MoSi-based halftone mask.